Multi-Scale Wavelet Analysis of Okavango River discharge patterns at the Mohembo station upstream the Okavango Delta, Botswana

Abstract

Analysis of temporal variability of Okavango River discharge time series is important in revealing the hydrological processes and processes in a semi-arid system. The aim of analyzing the discharge patterns was to determine periodicities and temporal evolution of stream flow regime of the transboundary Okavango River system over a 90-year time series (1930 – 2020). Using the Daubechies wavelet transform for multiresolution decomposition, several significant periodicities at multiple temporal scales were identified. The analysis revealed dominant cycles across varying timescales; semi-annual (0.5 years), annual (1-year) and multiyear (8 and 10 years) cyclic patterns suggesting complex hydroclimatic influences from the upstream Angolan highlands. Cross-wavelet analysis between the river discharge and precipitation in the headwaters highlighted the evolution of the identified periodicities and their spatial coherence across the transboundary basin. Of particular significance was the discharge patterns which showed declining flows over time due to the absence of historically prevalent peak flows in recent decades. The findings provide vital insights which would enable better prediction of flow patterns to inform adaptive management strategies and sustainable use of the available water resources. With the growing hydroclimatic uncertainty in the region, the periodicities and temporal patterns provide a basis for improving resilience of water management systems.